I. Field of the Invention
This application is directed to aqueous neoprene based contact adhesives characterized by superior metal adhesion and water and heat resistance.
II. Brief Description of the Prior Art
Solvent based polychloroprene or chloroprene-containing copolymers (commonly referred to as ("neoprene") adhesives have long been known in the art. These adhesives are often formulated as contact adhesives and, as such, are characterized by superior properties in areas as water resistance and metal adhesion. These adhesives are also characterized by a long bonding range or "open time", which means that there is a relatively long period after the adhesive is dry during which adhesive coated members can be successfully joined and bonded; suitable heat resistance, which refers to the ability of the bonded assembly to withstand elevated temperatures without lifting or deformation; and high immediate strength, which permits the bonded assembly to be handled and utilized within a reasonable time. In order to eliminate fire hazards and other environmental problems associated with these solvent based adhesives, attempts have been made to prepare these neoprene adhesives as latex systems (see, for example, U.S. Pat. No. 3,425,978). However, when the solvent based neoprene systems were replaced by latex based systems, the resulting contact adhesives were found to be inferior in quality, due primarily to their reduced metal adhesion particularly after exposure to moisture containing environments. Moreover, the heat resistance and "open time" were, in general, also inferior when compared with solvent based adhesives. For instance, where sufficient heat resistance is attained, the adhesives are deficient in bonding range, that is, the time after drying during which they can be pressed together and still form a suitable bond is too short for practical production applications. When the adhesive is formulated so as to lengthen the bonding range, the adhesive bond generally lacks sufficient rigidity, resulting in low initial strength and low shear strength, especially at elevated temperatures.
It is therefore an object of the present invention to provide an aqueous neoprene contact adhesive characterized by improved metal adhesion, heat and water resistance as compared to conventional neoprene latex adhesives; which properties are, in some instances, superior to that heretofore achieved with the solvent based systems.
It is a further object of the invention to provide an aqueous contact adhesive possessing a high degree of heat resistance without loss of open time.
These and other objects will be achieved in accordance with the invention described below.